Well, apart of answer that You've already got from OVK and tecs, reason - in my case - is simple. I always have my N900 with me. *Always*. And you know murphy law, you can have with you (even smallest) second camera, then, after half of an year, when You won't have it for one day, a plentora of interesting photo opportunities manifest themselves. It's exactly same with heavy tripods - they're great, powerful, stable, etc, but you never have them when You really need it. So I'm using ~0,3 kg modified tripod, that suits both my photo and video needs.

When comes to NightVision device (not photos - I mean viewfinder), it's even more clear - most of the time, you aren't carrying Night vision goggles with you, yep? NightVision photography is quite different things, cause You prepare for it (most of the times) - yet, it's still super cool to have it on N900 itself.

Of course, I admit that modding-fun is great part of why the heck bother". I also agree that it would probably cost the same - minus time spent on modding - to buy ready device (yet, i must admit that I've spent almost no money on mods, except some glue, and 0,1$ parts - I'm basically self-manufacturing everything, including tripod mount itself). Well, I could say that - at least - I don't need to explain my wife why we need IR capable camera or Night Vision device

But the truth is, that modifying it, and achieving such "unbelievable" things in our N900 is a lotta hell of fun. Just ask freemangordon, why he's working on 720p video recording and viewing, while camcoders of such capabilities can be bought cheap. Damn, if we already got those mini, wideangle Tessars (that probably are too small to benefit from 5 MP anyway - fixme?), lets use it fully!

/Estel

// Edit

Should be totally trivial to write for even moderately experienced coder (which, unfortunately, I'm not). Even with trigger only on user-set dB - there are many chunks of code available for it in our extras/garage projects.

// Edit 2

Tecs, I haven't commented about Your lossless digital zoom idea, because I haven't anything of value to say about that (thus only "Thanks" button pressed) - sounds nice, but totally out of scope for my skills, to even think about way of implementing. I wonder though, if it is even possible to implements using fCam libraries (as for camera-ui(2), it's probably not, as it's using what we already got by libraries and modules, modifying GUI side).